Researches on diamagnetism and magne-crystallic action : including the question of diamagnetic polarity / by John Tyndall.
- Tyndall, John, 1820-1893.
- Date:
- 1870
Licence: Public Domain Mark
Credit: Researches on diamagnetism and magne-crystallic action : including the question of diamagnetic polarity / by John Tyndall. Source: Wellcome Collection.
Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.
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![will be in the former line, which therefore will signalise itself between the poles, in a manner similar to the bismnth or iron wire ? The case seems analogous to that of good and bad conductors in electricity. This fluid will not quit the good conductor to go to the bad. The powder magazine is safe, because the fluid prefers the iron rod to any other path. As regards magnetism, different directions, through the same body, may represent these good and bad conductors; the line of preference being that of closest contact among the material par- ticles. [The illustration is not a good one.—J. T. 1870.] If analogic proof be of any value, we have it here of the very strongest description. For example :—bismuth is a brittle metal, and can readily be reduced to a fine powder in a mortar. Let a teaspoonful of the powdered metal be wetted with gum- water, kneaded into a paste, and made into a little roll, say an inch long and a quarter of an inch across. Hung between the excited poles, it will set itself like a little bar of bismuth—equa- torial. Place the roll, protected by bits of pasteboard, within the jaws of a vice, squeeze it flat, and suspend the plate thus formed between the poles. On exciting the magnet the plate will turn, with the energy of a magnetic substance, into the axial position, though its length may be ten times its breadth. Pound a piece of carbonate of iron into fine powder, and form it into a roll in the manner described. Hung between the ex- cited poles, it will stand as an ordinary magnetic substance— axial. Squeeze it in the vice and suspend it edgeways, its po- sition will be immediately reversed. On the development of the magnetic force, the plate thus formed will recoil from the poles, as if violently repelled, and take up the equatorial position. We have here s approach' and ' recession/ but the cause is evident. The line of closest contact is perpendicular in each case to the surface of the plate—a consequence of the pressure which the particles have undergone in this direction ; and this perpendicular stands axial or equatorial according as the plate is magnetic or diamagnetic. We have here a * directive force,' but it is attraction or repulsion modified. May not that which has been here effected by artificial means occur naturally ? Must it not actually occur in most instances ? for, where perfect ho- mogeneity of mass does not exist, there will always be a prefe- rence shown by the forces for some particular direction. This](https://iiif.wellcomecollection.org/image/b21167096_0044.jp2/full/800%2C/0/default.jpg)
